1. Field of the Invention
The invention relates to a device for delivering reducing agent from a tank to a metering unit. Such delivery devices are increasingly used, in particular in the case of mobile internal combustion engines, for delivering reducing agent into an exhaust-gas treatment device. The invention also relates to a motor vehicle having the device.
Exhaust-gas treatment devices with which a reducing agent is injected into an exhaust line are used for the purification of exhaust gases of internal combustion engines. In exhaust-gas treatment devices of that type, a purification of the exhaust gases takes place through the conversion of pollutant constituents of the exhaust gas with the supplied reducing agent. A particularly commonly used method is the method of selective catalytic reduction (SCR). In that method, nitrogen oxide components in the exhaust gas are converted, with the reducing agent, into harmless components such as nitrogen, water and carbon dioxide. Ammonia is preferably used as a reducing agent for that purpose.
In particular, in the case of mobile internal combustion engines, ammonia is stored not directly but rather in the form of a reducing agent precursor. Such a reducing agent precursor may, for example, be urea, and in particular a urea-water solution. A urea-water solution with a urea content of 32.5% is already widely available under the trademark AdBlue.
In order to deliver the reducing agent precursor from a tank provided therefor into an exhaust-gas treatment device, a delivery device is generally required. Delivery devices with pulsatingly operating delivery pumps such as, for example, piston pumps or diaphragm pumps, have become established for reasons of reliability and/or costs. A disadvantage of pulsatingly operating delivery pumps (that is to say, in particular, intermittently operating delivery pumps or delivery pumps which deliver through the use of a stroke movement) is that they generate a delivery noise. However, for comfort in a motor vehicle, it is desirable for the delivery of the reducing agent to take place with the least noise possible.
Furthermore, high dosing accuracy of the supplied reducing agent into the exhaust-gas treatment device is desirable. That is the case firstly because an exact predefined quantity of reducing agent should be supplied into the exhaust-gas treatment device for the conversion of the pollutant constituents in the exhaust gas, and secondly because the consumption of reducing agent during the operation of the exhaust-gas treatment device should be as low as possible. The consumption of supplied reducing agent represents a cost factor for the operation of the motor vehicle. Furthermore, the reducing agent constitutes an additional operating medium which the user of a motor vehicle must replenish separately. It is often sought by the manufacturers of motor vehicles to dimension the reducing agent reservoir in a motor vehicle so as to be sufficient for the entire operating interval of the motor vehicle between two workshop or garage intervals. The user of the motor vehicle is then not burdened with replenishing the reducing agent stored in the motor vehicle.